|  | 4.4 | Explain Layer 2 Design
| 4.4.4 |
Determining the number of cable runs and drops
By installing LAN switching at the MDF and IDFs and vertical cable between the MDF and the IDFs, the vertical cable is carrying all the data traffic between the MDF and the IDFs; therefore, the capacity of this run must be larger than that of the runs between the IDFs and workstations. Horizontal cable runs use Category 5 UTP, and no cable drop should be longer than 100 meters, which allows links at 10 Mbps or 100 Mbps. In a normal environment, 10 Mbps is adequate for the horizontal cable drop. Because asymmetric LAN switches allow for mixing 10-Mbps and 100-Mbps ports on a single switch, the next task is to determine the number of 10-Mbps and 100- Mbps ports needed in the MDF and every IDF. This can be determined by going back to the user requirements for the number of horizontal cable drops per room and the number of drops total in any catchment area, along with the number of vertical cable runs. For example, say user requirements dictate that 4 horizontal cable runs be installed to each room. The IDF that services a catchment area covers 18 rooms. Therefore, 4 drops ×18 rooms = 72 LAN switch ports.
| Threaded Case Study
Washington Project: LAN Topology Requirements

As you're planning the LAN topology for your school site, you need to keep in mind certain requirements for rooms that need access to the network and the room's wiring POP.

Requirement 1
Each room requiring connection to the network needs to be able to support 24 workstations and be supplied with four Category 5 UTP runs for data, with one run terminated at the teacher's workstation. These cable runs should be terminated in the closest MDF or IDF. All Category 5 UTP cable runs need to be tested end-to-end for 100 Mbps bandwidth capacity.

Requirement 2
A single location in each room needs to be designated as the wiring POP for that room. It needs to consist of a lockable cabinet containing all cable terminations and electronic components that is, data hubs or switches). From this location, data services need to be distributed within the room via decorative wire molding. Network 1 needs to be allocated for general curriculum use, and Network 2 needs to be allocated for administrative use.